Experimental diagnosis of electron density and temperature in capacitively coupled argon plasmas: Triple-frequency discharges and two-dimensional spatial distributions

Abstract

Effects of radio-frequency power and driven frequency on the two-dimensional (axial and radial) distributions of electron density and temperature were experimentally investigated in low pressure capacitively coupled argon plasmas. The intensity profiles of 696.5 nm and 750.4 nm emission lines were detected by employing a spatially resolved diagnostic system, which consists of a charge coupled device (CCD) and bandpass interference filters. The two-dimensional distributions of electron density and electron temperature were calculated from the spatial distributions of emission intensities via a collisional radiative model (CRM). It is found that the axial and radial distributions of electron density are more uniform at a lower RF power. The axial uniformity of electron density is better at a lower driven frequency, while the radial profiles of electron temperature is flatter at a higher excitation frequency. In all the cases, the electron temperature is extremely uniform in the bulk plasma. Moreover, a mode transition from the α to the γ mode is observed with the increase of input RF power at 13.56 MHz, which causes a significant increase of electron density and an abrupt decrease of electron temperature.

A novel capacitively coupled plasma driven by hollow cathode radio-frequency discharges

“…And optical emission spectroscopy with the argon collision-radiative model (OES-CRM) developed previously [24] was also used to obtain electron temperature and density. The irradiance mode of an optical emission spectrometer (Avaspec-2048TEC) can be used to monitor light intensity at the center of the discharge.…”

Atomic spectrometry update: review of advances in atomic spectrometry and related techniques

“…A Voigt function was fitted to the H α line profiles because the Gaussian part of the line profile was 0.44 Å, which corresponded to the convolution of the instrumental width and the Doppler width for 10 000 K. Values of n e were between (1.24 and 1.37) × 10 16 cm −3 for DC arc plasmas and (1.69·and 1.80) × 10 17 cm −3 for pulsed arc plasmas. The T e values ranged from 9100 to 13 600 K. The n e and T e of a low pressure, Ar CCP was determined by Wu et al 104 using OES and a CR model. They found that in triple-frequency (2, 13.56, and 27.12 MHz) plasmas n e was more independent of T e , compared with dual-frequency (2 and 27.12 MHz) plasmas, as the intermediate frequency power increased.…”

Kinetic simulations of capacitively coupled plasmas driven by tailored voltage waveforms with multi-frequency matching

“…However, it was found that the change of voltage amplitude or frequency could not independently regulate the ion flux and the mean ion bombardment energy (IBE), thus dual-frequency CCPs that decouple these two key parameters are proposed [5,6]. Many advantages of dual-frequency CCPs have been demonstrated [7,8]. Typically a high low-frequency voltage is used to control the IBE as compared to the low high-frequency voltage that controls the ion flux.…”